Peritoneum metastasis (PM) as a prognostic factor for anti-PD-1/PD-L1 monotherapy in metastatic gastric cancer (MGC)

Abstract

Anti-PD-1 monotherapy has proven effective for the patients (pts) with MGC. However, the identification of biomarkers for predicting clinical outcomes remain as critical needs. We aimed to identify baseline characteristics associated with time to treatment failure (TTF) or overall survival (OS) for anti-PD-1/PD-L1 monotherapy as second- or later-line in MGC. Routine blood count parameters and clinical characteristics at baseline were retrospectively investigated in 31 pts with MGC in Aichi Cancer Center Hospital. Endpoints were TTF and OS following anti-PD-1/PD-L1 monotherapy. Kaplan-Meiyer and Cox regression analysis were applied for survival analyses. Patient characteristics were as follows: median age (range), 68 (47-83); ECOG PS 0/1, 21/10; PM +ve/-ve, 12/19; No. of prior chemotherapy regimens 1-2/≥ 3, 11/20; and absolute eosinophil count (AEC) < 150/≥ 150/µl, 14/17. Objective response rate and disease control rate were (RECIST ver. 1.1) 26% vs. 0% (odds ratio [OR], 3.76; P = 0.12) and 79% vs. 50% (OR, 3.58; P = 0.12) in the PM -ve group (Cohort A) and the PM +ve group (Cohort B). On univariate analysis, the pts with poor PS, PM +ve, and high AEC were significantly poor TTF; and poor PS and PM +ve were significantly identified as prognostic factors of poor OS. On multivariate analysis, only PM +ve was independent negative impact not only for TTF but also for OS. Median TTF and OS were 5.4 vs. 1.3 months (M) (adjusted hazard ratio [HR], 4.29; 95% CI, 1.60-11.5; P < 0.01) and 28.2 vs. 7.5 M (adjusted HR, 3.68; 95% CI, 1.25-10.8; P = 0.02) in Cohort A and Cohort B. Six-months TTF probabilities of 42% vs. 0% (P = 0.03) and one-year OS probabilities of 58% vs. 8% (P < 0.01) were observed in Cohort A compared to in Cohort B. PM -ve in the pts treated with anti-PD-1/PD-L1 monotherapy was associated with better efficacy. In the pts with PM -ve, anti-PD-1/PD-L1 monotherapy could be adapted in first-line therapy.